1. Field of the Invention
The present invention relates to a pneumatic drilling device, and more particularly, to a pneumatic drilling device suitable for the drilling process of composite materials.
2. Description of the Related Art
In recent years, CFRP (Carbon Fiber Reinforced Plastics) have been used in aircraft parts or the like, and composite materials such as CFRP/Aluminum and CFRP/Titanium has been increased.
However, it is known that high-precision drilling of such composite materials is difficult due to the differences in cutting conditions. Therefore, for example, there is employed a drilling method for maintaining the advance per revolution of a spindle constant by synchronizing feed and rotation with a single motor (for example, see Japanese Published Unexamined Patent Application Nos. 2005-161452 and 2008-110473). That is, variations in speed of the motor have no effect on the rate of advance per revolution, and therefore the thickness of the swarf formed remains constant, thereby promoting the surface quality and precision of the drilled holes.
However, when feed and rotation is synchronized by a single motor, the feed rate is fixed, and, in the case of composite materials, the feed rate is determined according to the conditions of firm materials. Thus, in the past, there has been a problem that a lot of machining time is required. Further, when spindle rotation speed is reduced under load, the feed rate is also reduced in synchronization, and therefore a lot of machining time is required again. In addition, cutting is performed at a feed rate set regardless of wear and tear on a cutting tool. This might cause not only the reduction in processing quality but also the breakage of a workpiece.